1. Field of the Invention
The present invention relates generally to static structures, particularly traffic-carrying surfaces, and also relates to exercising devices, particularly gymnastic equipment, such as a children's play mat.
2. Description of the Related Art
School playgrounds, day care centers, playlands adjacent to fast food restaurants, and the like maintain exercising equipment for children's recreational activities. The activities in these designated play zones include climbing, jumping and swinging, and oftentimes result in falls to the ground. In fact, 70% of playground injuries are the result of impacts to the underlying surface.
In the past, natural grass was grown as a surface for use underneath playground equipment. Unfortunately, natural grass requires constant maintenance and varies in its shock attenuating ability. Furthermore, erosion, puddling and sanitation are major negative factors militating against the use of natural grass.
In the search for an answer to the problems posed by natural grass, two generic categories of surfacing used under all types of play equipment were defined: loose-fill and nonloose-fill. Loose fill surface systems consist of nonbonded particles, usually of a common type (e.g. sand, wood chips, etc.). Nonloose-fill surface systems consist of processed particles bonded together in some fashion (e.g. foam blocks, rubber-aggregate blocks together, etc.).
Loose-fill materials are generally placed under playground equipment to a depth averaging twelve inches and are usually contained by a wooden or concrete border. Although loose-fill materials provide excellent attenuating characteristics, it is difficult to maintain them at the proper depth and to keep them free of contamination. Changes in depth and infiltration by debris and water adversely affect the attenuating properties of such loose-fill materials. Furthermore, loose-fill surface systems tend to absorb dirt, debris, and toxins from the air, and water. Since small children oftentimes ingest loose-fill materials during play, constant replacement of such loose-fill materials is necessitated. Water, when absorbed into the loose-fill material, causes accelerated deterioration during normal use and freezing below 32.degree. Fahrenheit.
With a desire for a more permanent and consistent, nonloose surface, nonloose-fill surface systems were developed to be installed over hard surfaces, such as concrete and asphalt. Nonloose-fill surfaces, which are generally referred to as synthetics, can be divided into two main categories: systems with seams and systems without seams. Examples of systems with seams or so-called nonseamless systems are shown in U.S. Pat. No. 4,557,457 to Donovan, U.S. Pat. No. 3,846,945 to Roby, U.S. Pat. No. 3,251,076 to Burke, U.S. Pat. No. 2,999,431 to Mitchell, and U.S. Pat. No. 957,387 to Stedman.
Both nonseamless and seamless surfacing systems have an attenuating element and a surface layer. This surface layer can be either installed in the field or integrated at the time of manufacture. However, the seamless systems have a texture coat of sealer and aggregate applied over the surface layer to form a monolithic arrangement.
Seamless surfacing systems are becoming the more desirable of the synthetic systems because insects and rodents cannot enter and nest in them, nor can dirt and debris collect in the seams. An additional benefit of seamless surfacing systems is that water is not allowed to enter into the system. Water, when introduced into the system, can cause structural deterioration, can cause delamination of the surface system from its subbase, and can cause the seamless surface system to freeze much more quickly and intensely in play conditions below 0.0 degrees Celsius.
Finally, the recognized methodology for testing the shock attenuating properties of playground and athletic surfacing systems is the American Society for Testing and Materials (hereinafter ASTM) F-355 test which uses three different missiles at impact velocities appropriate for the intended end-use: Procedure A uses a cylindrical missile, weighing twenty pounds and having a circular, flat, metallic, impacting face of twenty square inches; Procedure B, uses a metallic hemisphere weighing fifteen pounds and having an impacting surface with a radius of 3.25 inches; and third, Procedure C, uses a metallic headform weighing eleven pounds (five kilograms).
The report section within the ASTM F-355 test methodology lists various ways to collect and analyze data. The two most important measurements of the shock attenuating characteristics of a surfacing system are: (A) the G-max which is the maximum acceleration experienced over the duration impact, and (B) the Severity Index which is an integration of the G-max over the duration of the impact. The G-max represents the maximum stress point experienced by the impacting body over the duration of the impact; the Severity Index represents the total stress experienced by the impacting body over the duration of the impact. A G-max of 200 and a Severity Index of 1,000 are internationally recognized as the threshold for skull concussion with respect to human beings.
In Apr., 1981, The Consumer Products Safety Commission (hereinafter CPSC) published Guidelines For Public Playground Equipment, Volumes I and II. In Volume II, page 22, Sections 12.1-12.5, the CPSC recommends use of a surface system under public playground equipment that will not exceed a 200 G-max when tested as per the ASTM F-355 test; Procedure at the maximum estimated fall height of a piece of playground equipment. Since their publication, the CPSC's surface system guidelines have been used by a significant number of both public and private playground operators that are concerned about playground safety.
The ASTM is presently finishing a Standard Specification for surface systems used under playground equipment and is based on the CPSC's Guidelines for surface systems. The ASTM's Standard Specification for surface systems, when published, will clearly define a laboratory test procedure and a field test procedure within a specified temperature range for all loose-fill and nonloose-fill surface systems.
The ASTM's Standard Specification will provide the consumer with a convenient tool with which he or she can measure and specify the performance and quality of all types of playground surface systems.
Future editions of the ASTM's Standard Specification for surface systems used under playground equipment will undoubtedly require, in addition to a maximum G-max value of 200, a maximum Severity Index value of 1000. The Severity Index relates principally to human head injuries which are the most damaging and difficult to treat.
As the level of consumer awareness rises and technological advances in manufacturing continue to increase, performance guidelines will transform into future product standard specifications. The British Government currently mandates a G-max value of less than 200 and a Severity Index value of less than 1000, utilizing the ASTM F-355 test, Procedure B, for surface systems used under playground equipment in the United Kingdom.